Residual induced-radioactivity at the old 160 cm cyclotron

Abstract

The old 160 cm cyclotron built in 1966 at RIKEN (Institute of Physical and Chemical Research), which has been already shutdown though, still contains induced radioactivity. For estimating the amount of the radioactive waste from this cyclotron, several samples were taken from it, and the induced radioactivity of the samples was measured with a Ge detector for the gamma ray spectrometry. The results of the measurement were summarized in a table. The measured radioactivity is only Co-60 for the most samples. The radioactivity of Fe-55 and Ni-63 radionuclides expected in the iron and copper material, which could not be detected by the Ge detector, was also estimated and discussed. The concentration of 0.2 Bq/g of Co-60 was considered as non-radioactive. On this criterion, the substances of the diffusion pump and the iron at resonator are all treated as radioactive. Iron and copper parts placed far from the beam orbit are non-radioactive, while almost all parts of the stainless steel are radioactive.

RIKEN(理化学研究所)での1966年に建造した古い160cmサイクロトロンは既に停止しているが、なおも誘導放射能を含んでいる。このサイクロトロンからの放射性廃棄物の量を推定するために、これから数サンプルを取り、これらのサンプルの誘導放射能をガンマ線分光法用のGe検出器で測定した。測定結果は1つの表にまとめた。測定した放射能は大部分のサンプルでCo-60のみである。Ge検出器で検出できない、鉄と銅物質に期待される核種Fe-55とNi-63の放射能も推定し、議論した。0.2Bq/g濃度のCo-60は非放射性と考えた。この基準により、拡散ポンプの物質や共振器での鉄はすべて放射性として取扱われる。ビーム軌道から離れたところにある鉄と銅の部分は非放射性で、すべてのステンレス鋼の大部分は放射性である。